The present invention relates generally to aspirating face seals for rotor and stator assemblies and, more particularly, to rotatable and non-rotatable gas bearing face surfaces of aspirating face seals with pull off springs to retract the non-rotatable gas bearing face surface away from the rotatable gas bearing face surface during periods of low pressure differentials across the seal.
Aspirating face seals are used to minimize leakage through a gap between two components and from a higher pressure area to a lower pressure area. Such seals have been disclosed for use in rotating machinery, including, but not limited to, turbomachinery such as gas turbine engines used for power generation and for aircraft and marine propulsion. Aspirating face seals are designed to minimize leakage of a fluid such compressed air or combustion gases between a rotor and a stator in gas turbine engines.
Conventional aspirating face seals typically have the rotor configured as oppositely facing rotatable and non-rotatable seal elements, with the rotatable seal element either being attached to, or being a monolithic portion of the rotor. Such seals typically have the non-rotatable seal element configured being axially movably attached to a portion of the stator. The rotatable and non-rotatable seal elements are generally annular, generally perpendicular to the longitudinal axis of the rotor, generally opposing, axially spaced apart, and proximate each other.
Typically, the first rotatable and non-rotatable elements together define a radially extending air bearing and a radially extending air dam positioned radially inward of the air bearing. An air bearing surface of the first element and an air dam surface of the first element generally lie in the same plane. The air bearing surface of the second element has a hole which is an outlet for a first passageway connecting the hole with air from a higher pressure side of the seal. The stator has a second passageway which carries air, which has passed the air dam from the higher pressure side of the seal, to a lower pressure side of the seal. Known seal designs have also included an aspirator tooth extending from the stator axially across, and radially inward of, the air dam, with the aspirator tooth having a tip spaced apart from and proximate the rotor. It is also important to note that aspirating face seal technology uses phrases such as xe2x80x9cair bearingxe2x80x9d, xe2x80x9cair damxe2x80x9d, and xe2x80x9cair flowxe2x80x9d, wherein it is understood that the word xe2x80x9cairxe2x80x9d is used to describe the working fluid of the seal. The working fluid of an aspirating face seal can include, without limitation, compressed air, combustion gases, and/or steam. Reference may be had to U.S. Pat. Nos. 5,311,734 and 5,975,537 for more details on aspirating face seals and their operation.
Many aspirating face seals use multiple coil springs positioned circumferentially around a portion of the stator for urging the non-rotatable seal element and its non-rotatable gas bearing surface away from the rotatable seal element and its rotatable gas bearing surface when the engine is not running or when the pressure differential across the aspirating seal is low. The multiple spring concept includes many non-axisymetric parts which are exposed to the severe operating environment of a gas turbine engine. This includes significant dust which at high velocity can quickly erode away the material of interrupted features like coil springs. Some seals do not use springs and may allow rubbing of the rotor and stator elements each time the engine is started causing premature part wear out.
It is important to note that an aspirating face seal is a non-contacting seal in that the first and second parts of the seal are not suppose to touch but could for short periods of time during which they experience what are known as rubs. Aspirating face seals generate significant heat and/or scratch rotor surfaces when seal rubs occur. It is, thus, desirable to minimize heat input into the rotating component and maintain a smooth surface flush. Excessive heat input into the rotor component can result in material degradation which in turn can lead to premature component crack initiation. A rough surface finish could result in excessive seal leakage and create a stress riser, which could also cause premature component crack initiation.
A gas turbine engine aspirating face seal includes a rotatable engine member and a non-rotatable engine member and a leakage path therebetween. An annular generally planar non-rotatable gas bearing face surface is operably associated with the non-rotatable engine member and an annular generally planar rotatable gas bearing face surface is operably associated with the rotatable engine member. The non-rotatable and rotatable gas bearing face surfaces is circumscribed about and generally perpendicular to a centerline axis. A substantially fully annular pull off biasing means is operably disposed for urging the non-rotatable gas bearing face surface axially away from the rotatable gas bearing face surface and circumscribed about the centerline axis. The pull off biasing means may be at least one wave spring or one bellville washer. The non-rotatable gas bearing face surface may be on a face seal ring mounted on a translatable cylindrical piston which is axially movable and supported by the non-rotatable engine member. The spring chamber may be formed in part by radially extending static and axially movable flanges attached to a face seal support structure and the translatable cylindrical piston respectively, wherein the face seal support structure is supported by the non-rotatable engine member. The rotatable engine member may be a rotor disk or, in a more particular embodiment, the rotatable engine member is a side plate mounted on a rotor disk and the non-rotatable gas bearing face surface is on a face seal ring mounted on a translatable cylindrical piston which is axially movable and supported by the non-rotatable engine member.
The seal may further include an auxiliary seal having a restrictor tooth radially spaced apart from and proximate to a seal land disposed between the rotatable engine member and non-rotatable engine member. More particularly, the seal may further include an auxiliary seal disposed across the leakage path radially inwardly of the gas bearing face surfaces. The auxiliary seal may include an annular restrictor tooth radially spaced apart from and proximate to an annular seal land having an annular auxiliary seal surface circumscribed around the engine centerline axis.
The seal may include radially inner and outer tooth rings axially extending away from a first one of the gas bearing face surfaces across the leakage path and towards a second one of the gas bearing face surfaces. An annular plenum is located between the inner and outer tooth rings and a portion of the first gas bearing face surface between the inner and outer tooth rings. Alternatively, the seal may include a primary restrictor dam radially spaced apart from the non-rotatable gas bearing face surface by an annular vent channel.